The project entails efforts to develop and refine techniques for the preparation, maintenance, and characterization of cultures of dispersed neurons obtained from the dorsal root ganglia (DRG) and spinal cords (SC) of chick embryos. Current work is focused on development and application of various approaches to the characterization of neurons surviving in the cultures. Use of 3H-thymidine-labeled donor embryos and subsequent culture radioautography to define "birthdate spectra" for the surviving neurons is being explored as an approach to determining whether preparative protocols or culture environments select for particular sub-populations of neurons from the tissues of origin. A combination of extra- and intracellular electrophysiological techniques as a "screening-test" for functional synaptic connections among cultured neurons is under study as are various parameters for the characterization of intracellular records that seem likely to be freer than those commonly employed of artifactual variation arising from membrane injuries inflicted by the recording electrode. Also, immunohistological approaches to distinguishing different types of neurons in mixed cultures are under investigation. It is hoped that the cultures themselves and the analytical techniques being developed to characterize them will both eventually be suitable and adequately defined for studies comparing the properties displayed by neurons cultured under selected conditions (e.g., in the presence or absence of nonneuronal cells or of specific, presumptive synaptic partners) to those of the same types of neurons in vivo and for studies of the formation, maintenance, specificities and function of synapses between neurons.